1. Field of the Invention
The present invention relates to an apparatus constituted by a plurality of dispensing assemblies for automatically preparing and dispensing espresso coffee, each assembly of the plurality being of the type comprising:    a cylinder member which has a chamber for containing a predetermined measure of coffee grounds, which has a closed base and which is provided with an open top, and a piston member, which are each provided either with an opening for dispensing the beverage prepared or, as an alternative with means for supplying heated and pressurized water to the cylinder member in the chamber for preparing the beverage;    said cylinder member and said piston being pivotable relative to each other between a position for charging and discharging the measure of coffee grounds, before and after the beverage is dispensed, respectively, and a position in which the cylinder member and the piston member are in alignment;    said piston member being movable in relative terms in order to close and open the chamber by moving into and out of the cylinder member;    a pair of mutually opposing and spaced-apart walls defining an intermediate space in which the cylinder member and the piston member are housed and supported;    a kinematic arrangement having a connecting rod and crank for causing said cylinder member or said piston member to swing and for moving either the piston member or the cylinder member in the prescribed operating sequence, that kinematic arrangement comprising a pair of connecting rods which are connected, at one end, to the sides of the piston member or of said cylinder member and, at the opposite end, to a respective crank which is supported by a respective wall of said opposing walls, the cranks being rotationally rigidly connected to each other;    and motor means for actuating at least one of the cranks and cam members for the angular displacement of the cylinder member and the piston member.
2. Description of Related Art
In accordance with the prior art, in completely automatic devices in which the operator does not carry out any manual operation, the assemblies for dispensing the coffee are normally provided with a cylinder body chamber whose volume is such to be able to also contain a quantity of coffee grounds equal to twice that necessary for preparing and dispensing a single coffee. However, if the diameter of the chamber remains constant, the quantity of two measures of coffee grounds necessarily leads to an increase in the thickness of the layer which will have to be passed through by the pressurized hot water which is introduced into the chamber when the request is made for a double coffee to be dispensed.
Since an essential condition for making a good espresso coffee is the constancy of the dispensing time which has to be maintained at approximately 25 seconds, irrespective of whether one measure or two measures of the beverage are being dispensed, the flow rate of the dispensing water must consequently be, when two measures of coffee are dispensed, double the flow rate used when a single measure is dispensed.
In the case of an automatic dispensing assembly of the type mentioned above, as is evident, the double measure of coffee grounds involves the formation of a double layer with respect to that which is present for a single measure. Consequently, given equal fineness of the grounds, in an identical chamber provided with a filter having holes of a given diameter, the same times for preparing the beverage cannot be maintained when varying the measure.
In order to overcome the differences in flow rate brought about by the use of one measure or two measures of coffee grounds, use is made, in accordance with a first solution of the prior art, of a quantity of coffee grounds greater than necessary for producing the single measure and a lesser quantity of coffee grounds when constituting the measure for two coffees, with the fineness of the grounds further being controlled at an intermediate granule size between one which optimizes the dispensing of a single measure and one which optimizes the dispensing of a double measure.
In accordance with another arrangement of the prior art, the problem presented by the automatic assemblies for dispensing coffee, there is used, downstream of the filter, a valve for limiting the flow rate whilst another arrangement in the prior art consists in varying the fineness of the grinding of the coffee as a function of the quantity of grounds which has to be used, as set out, for example, in EP 0 100 030. It is evident that the solutions proposed by the prior art are fundamentally based on a compromise to the detriment of the quality of the beverage.
In markets where the culture of espresso coffee is firmly established, since the above-described known solutions are not sufficient to ensure constant quality comparable with that obtained by a manually operated machine, in which adaptation to the conditions for dispensing one measure or two measures of coffee is carried out manually by changing the filter, the introduction of machines having automatic dispensing assemblies encounters serious difficulties.